Especially in the case of machine tools used for mass production, for example, the mass production of screws or bolts, productivity is determined by the weakest link in the production train. In the manufacture of screws, for example, this weak link has been in the past the stamper, plunger or ram of the press which had to be replaced after a relatively limited run. The press run, depending upon the particular product and the material from which the product was made, could amount to 30,000 to 250,000 pieces.
In a high-capacity press, capable of producing 800 pieces per minute, it was not uncommon to have to replace the ram or plunger tool every two hours. The replacement process was relatively time consuming and required that the apparatus be brought to a costly standstill, thereby limiting productivity.
To reduce the drop in productivity and to allow tool replacement with little investment in labor, it has been proposed to provide an automatic tool-replacement system. For this purpose, a number of identical tools, for example, stamping tools, were stored in a magazine and fed from the magazine to the tool holder. A mechanism was provided for removing a stamping tool from the tool holder, inserting it into the tool holder, removing the worn tool from the tool holder and placing it in the magazine and advancing the tool in the magazine to the replacement position. The tools could then be removed from the magazine for machining or refinishing.
The tool holder had to be arrested in a certain position for the tool change and, especially when the tool did not have a regular shape, there was always the danger that the tools in the magazine would jam against one another, delaying the withdrawal of a tool or the reinsertion of a worn tool into the magazine. As a consequence, in spite of the automatic tool replacement mechanism and the availability of a magazine with a store of replacement stamping tools, there was always the danger of delay in the tool chain and of a productivity drop.